Elastic Long-Chain Multication Cross-Linked Anion Exchange Membranes

Abstract

Anion exchange membranes (AEMs) are a promising class of materials that enable non-noble metals to be used as catalysts in fuel cells. Compared to their acidic counterparts, typically Nafion and other perfluorosulfonate-based membranes, the low OH– conductivity in AEMs remains a concern as these materials are developed for practical applications. Cross-linked macromolecular structures are a popular way to optimize the trade-off between the ionic conductivity and the water swelling of AEMs with high ion exchange capacities (IECs). However, common cross-linked AEMs (e.g., x(QH)­QPPO) that have high degrees of cross-linking with low molecular weight between cross-links are usually mechanically brittle. Moreover, the cross-links in AEMs can hinder the transport of OH–, leading to unsatisfactory conductivities. Here we report a series of elastic and highly conductive poly­(2,6-dimethyl­phenylene oxide) (PPO)-based AEMs (x(QH)3QPPO) containing flexible, long-chain, multication cross-links. The strength and flexibility of the x(QH)3QPPO samples are significantly improved as compared to the conventional x(QH)­QPPO membranes and multication un-cross-linked materials reported previously. The high conductivities in these new materials (x(QH)3QPPO-40, IEC = 3.59 mmol/g, σOH– = 110.2 mS/cm at 80 °C) are attributed to the distinct microphase separation observed in the x(QH)3QPPO membranes by SAXS and TEM analyses. Furthermore, the x(QH)3QPPO samples exhibit good dimensional (swelling ratio of x(QH)3QPPO-40 is 25.0% at 80 °C) and chemical (22% and 25% decrease in IEC and OH– conductivity in 1 M NaOH at 80 °C for 30 days, respectively) stabilities, making this cross-linking motif suitable for potential membrane applications in fuel cells and other electrochemical devices.

Utilizing thiol–ene chemistry for crosslinked nickel cation‐based anion exchange membranes

“…This seemed reasonable since the membranes were essentially fully hydrophobic. Interestingly, however, once nickel was added, a broad scattering peak appeared for all samples except for HP4‐5Ni , consistent with the formation of ionic clusters within the network, due to the formation of clustered metal cations . The lack of a second‐order peak indicated that the phase separation did not have long range order, and thus likely arose from ionic clusters.…”

“…Six different AEMs were fabricated, three with CP4 and three with HP4 as the crosslinker, where the amount of 3 added was modified so each membrane contained on average either 5, 10, or 20 repeat units of 3 , correlating to 5, 10, or 20 repeat units of nickel cations, between two PS crosslinkers. However, despite increasing the metal content, all three samples had IEC values of around 1 mmol/g, as determined by back titration . Full nomenclature and components of each membrane are shown in Scheme , where the first part of the name indicates which PS crosslinker was used and the number indicates the average repeat units of 3 .…”

Synthesis and Properties of Symmetric Side‐Chain Quaternized Poly(Arylene Ether Sulfone)s for Anion Exchange Membrane Fuel Cells

“…E a values of the 4C‐ y ‐Q membranes are approximately half those of the 8C‐ y ‐Q series, indicating better ion transport channel was established in the 4C‐ y ‐Q type membranes. Moreover, the activation energy barrier of 4C‐60‐Q is 6.61 kJ mol −1 , which is lower than that of Nafion 112 (7.02 kJ mol −1 ) and numerous reported AEMs, implying an obvious enhancement of ion transport in this novel symmetric side‐chain‐type ionomer.…”

“…σ/IEC values of 4C‐60‐Q and some reported membranes are shown in Figure . ANM‐22‐100 (IEC = 1.67 mmol g −1 ) and x (QH) 3 QPPO‐40 (IEC = 3.59 mmol g −1 ) membranes showed OH − conductivities comparable to those of Nafion 112 (IEC = 0.91 mmol g −1 ). However, their ionic conduction efficiency remained unsatisfactory.…”

A facile approach to prepare crosslinked polysulfone-based anion exchange membranes with enhanced alkali resistance and dimensional stability

“…At high temperatures, strongly electrophilic functional groups are more likely to be attacked by OH À . 2,46 Thus, the IEC retention ratios and conductivity retention ratios of the cross-linked AEMs (CAPSF-N) and APSF membrane sample were tested to evaluate their alkaline stability by calculating the ratio of IEC and the conductivity of the tested AEMs before and aer being soaked in 1 M KOH at 60 C for 15 days. As illustrated in Fig.…”